Proposed methods for carrying digital video programming from a Head End (HE) to a Set Top Box (STB), over a Digital Subscriber Line (DSL) connection, now exist within the industry. In many cases, the digital video is in the form of compressed digital video such as Moving Pictures Experts Group (MPEG) 2 or MPEG 4. Many of these systems utilize video multicast within the HE equipment for efficient distribution of the video to the edge of the network. An important limitation of these systems is that a DSL link has only enough bandwidth to handle one or two video streams (programs) simultaneously.
Because of the bandwidth limitation, one problem that these systems experience is jitter. Jitter is a deviation in, or displacement of, the bit arrival times of a digital signal. Some of the principle causes of jitter include, inter alia, queues in network switches and packet collisions requiring subsequent retransmission. Jitter may also be added to the video stream as the result of the asynchronous transfer mode (ATM) switching or Internet Protocol (IP) routing. Furthermore, jitter may occur as a result of adding to a video stream as the video is distributed within the home from the DSL modem to the STB'over, for example, an Ethernet.
Proposed methods for correcting jitter include, for example, the use of a large de-jittering buffer in the front end of the decoder in the STB. However, de-jittering buffers add a significant and undesirable time delay to the signal. For example, for a de-jittering buffer designed to hold five seconds of video, there would be a five-second delay from the time the video is received by the STB to the time that the video is displayed.
Buffering creates additional problems. For example, if a user changes channels and the system merely connects the STB to a real time video stream, the user will have to wait five seconds for the buffer to fill before a picture will be displayed. This would spoil the channel changing experience that many people expect. For example, many people like to “surf” channels to examine what is on a several particular television channels before settling on a program. Having a long delay each time a new channel is selected would be at odds with the ability to rapidly surf through the various offered channels, and these viewers would find such a delay particularly vexing.